Basic Knowledge About Fiber Optic Attenuator

It seems to be a commonplace for us to use an amplifier in fiber optic transmission which helps to improve signal electricity. However, it may occur sometimes that there is just too much light delivering through a fiber optic receiver and should better be reduced. In this case, a component known as fiber optic attenuator can help to reduce the power level of the signal. This article will focus on describing the fiber optic attenuator in details from the perspective of its types and applications.

What Is Fiber Optic Attenuator?

A fiber optic attenuator, generally known as optical attenuator, is a passive device used to reduce the power level of an optical signal. It can be adopted in both free space and in an optical fiber. Besides, to employ a fiber optic attenuator in single-mode long-haul application contributes to decreasing the chance of optical overload at the receiver.

By means of absorption, reflection, diffusion, scattering, deflection, diffraction and dispersion, etc, the fiber optic attenuator works efficiently to reduce the power of the signal. Optical attenuators usually function by absorbing the light, that resembles sunglasses absorb extra light energy. There exists a working wavelength range in which they absorb the light energy equally. They should not reflect the light since that could cause unwanted back reflection in the fiber system.

The Types of Fiber Optic Attenuator

There are a number of different forms of fiber optic attenuators by various classified methods, but basically, fixed attenuators and variable attenuators serve as the most common types that we can find in the market.

Fixed Attenuator

Fixed attenuator, as the name of which has indicated clearly, is designed to have an unchanging level of attenuation. It can theoretically be designed to provide any amount of attenuation that is desired. Fixed attenuator are typically used for single-mode applications and it consists of two groups: in-line type and connector type. In-line type appears like an ordinary fiber patch cable with a fiber terminated by two connectors. Connector type attenuator looks like a bulk head fiber connector, which has a male end and a female end as well. Fixed attenuator mates to regular connectors of the identical type such as FC, ST, SC and LC. The picture below shows a fixed male-female-SC/UPC SM 10dB fiber optic attenuator.

fixed attenuator

Variable Optical Attenuator

Variable optical attenuators generally use a variable neutral density filter. It has advantages of being stable, wavelength insensitive, mode insensitive, and offering a large dynamic range. Variable optical attenuator is generally used for testing and measurement, but it is also widely adopted in EDFAs (Erbium-Doped Fiber Amplifier) for equalizing the light power among different channels. Basically, there are two types of variable attenuators: stepwise variable attenuator and continuously variable attenuator. Stepwise variable attenuator can change the attenuation of the single in known steps such as 0.1 dB, 0.5 dB or 1 dB. Continuously variable attenuator produces precise level of attenuation with flexible adjustment. Thus, operators are able to adjust the attenuator to accommodate the changes required quickly and precisely without any interruption to the circuit. The following picture shows LC/UPC to LC/UPC variable fiber optic VOA in-line attenuator 0-60 dB.

variable optical attenuator

The Applications of Fiber Optic Attenuator

Fiber optic attenuator can be used to test power levels margins by temporarily adding a calibrated amount of signal loss. Besides, it is often installed permanently to properly match transmitter and receiver levels. And the sharp bends stress optic fibers and can cause losses.


From what we introduced above, you may have had a better understanding of the basic elements related to fiber optic attenuators. As an essential device in fiber optic transmission, it plays an indispensable role in controlling the power level of the optical signal. Those basic knowledge mentioned above may help provide a guideline to select the right fiber optic attenuator that matches the required applications precisely.